I previously invented a game board apparatus which is the subject of U.S. Pat. No. 3,653,668, issued Apr. 4, 1972. In accordance with the apparatus, geographic areas were divided into a number of pieces for the purpose of making a game. The pieces were similar in shape and were placed on the grid playing surface. They normally had indicia thereon relating one to another; but lacking such indicia they had no definite fixed relationship to one another in and of themselves. In several cases indicia on the playing surface related to particular indicia on a playing piece so that it was easier to place that piece on the board in the correct position than it was to place the run of the mill pieces which did not have such indicia on them.
One of the factors to be considered in playing the game in accordance with may prior invention is that a plurality of pieces can be placed on the board in incorrect positions even though they are related to one another, before the error is detected and the pieces are removed. Accordingly, it is desirable to have some means of readily detecting the error in piece placement, the instant that it is put in the incorrect position on the board; so that it can be immediately removed before the error is compounded by the placement of additional pieces.